Electrochemical behaviour of the pyrethroid insecticides

A systematic study is made of the electrochemical reduction and oxidation of eighteen pyrethroid insecticides and six model compounds. In addition the electrochemical oxidation of an insecticide synergist and the reduction of an insect repellent is studied. Oxidation and reduction mechanisms were partially or fully assigned for the the electrochemical reactions. The results indicate the presence of two oxidation sites common to the majority of pyrethroids. Specific sites of electrochemical reduction are observed for a number of pyrethroids. The electrochemical respones may be applied to the selective determination of a number pf pyrethroids synergists and repellents in commercial formulations without the requirement of pyrethroids, synergists and repellents in commerical formulations without the requirement for extensive sample preparation or the use of a separation technique.

Investigating the effect of solution pH on speciation of La(4OH-cin)3 with correlation to electrochemical behaviour and corrosion efficiency

The nature of the species in solution plays a major role on the effectiveness of the corrosion inhibitor on a steel substrate. The speciation of lanthanum 4-hydroxy cinnamate (La(4OHCin) ₃) in solution has been evaluated using experimental techniques composed of potentiodynamic polarisation, immersion tests, nuclear magnetic spectroscopy and mass spectroscopy. It is evident that the species in solution are dependent on pH and this impacts the corrosion inhibition mechanism and the efficiency. It was found that at a neutral pH of 5.5 the La(4OH-Cin)₃ behaves as a strong anodic inhibitor. Whereas, when the pH shifts to low (pH2.5) and/or high (pH8) the corrosion mechanism changes.

Electrochemical and spectroscopic investigation of redox processes for labile metal dithiocarbamate complexes

Although metal dithiocarbamate complexes have been studied extensively, there is in sate cases a distinct lack of data concerning redox properties and the products thereof. This is particularly true for complexes of the late transition and main group metals which are important in agriculture, industry, and chemical analysis. Hence, using electrochemical techniques, the redox behaviour of dithiocarbamate complexes of zinc, cadmium, mercury, lead, and tellurium has been examined. The products of oxidation and reduction have also been characterized by spectroscopic techniques (NMR, EPR, UV, and IR), mass spectrometry, conductivity, and Where possible, crystallographic study of an isolated compound. The species studied were without exception labile with the result that electrochemistry at mercury electrodes was influenced by the great stability of the mercury dithiocarbamate (Hg(RR’dtc) 2) complexes. Investigation of the latter showed that oxidative processes in the presence of mercury led to a new class of expounds: polymeric mercury dithiocarbamato cations. Oily one of these could be isolated as a solid, with the formula [Hg5(RR’dtc) 8](C104)2 For R=R’=ethyl the crystal structure was determined. For other metal dithiocarbamates the electrochemical behaviour at mercury electrodes in many ways paralleled that of the mercury analogues. Thus oxidative processes involved oxidation of electrode mercury to form mixed metal cationic species. Polarographic reduction led to the metal amalgam, usually via formation of mercury dithiocarbamate. Electrochemical studies at inert electrode materials such as platinum yielded distinctly different responses, with both oxidation and reduction being more difficult. Oxidation products at platinum electrodes gave identical polarographic responses to those firm mercury electrodes due to rapid interaction of the former with electrode mercury. The results are in sharp contrast to much of the previous work on transition metal dithiocarbamates for which electrochemical redox processes are often metal based arid not explicated by interaction with the electrode material.

Electrochemical investigation of sodium reactivity with nanostructured Co3O4 for sodium-ion batteries

The electrochemical behaviour of Co3O4 with sodium is reported here. Upon cycling in the voltage window of 0.01–3.0 V, Co3O4 undergoes a conversion reaction and exhibits a reversible capacity of 447 mA h g−1 after 50 cycles. Therefore, nanostructured Co3O4 presents feasible electrochemical sodium storage, offering possibilities to develop new anode materials for sodium-ion batteries.

Determination of rate constants using microelectrodes

An understanding of the rate and the mechanism of reaction is of fundamental importance in the many facets of chemistry. Electrochemical systems are further complicated by the heterogeneous boundary, between the solution and the electrode, that the electron passes through before any electrochemical reaction can take place. This thesis concerns the development of methods for analysing electrode kinetics. One part involves the further development of the Global Analysis procedure to include electrodes with a spherical geometry which are traditionally the most popular form of electrodes. Simulated data is analysed to ascertain the accuracy of the procedure and then the known artifacts of uncompensated solution resistance and charging current are added to the simulated data so that the effects can be observed. The experimental analysis of 2-methyl-2-nitropropane is undertaken and comparisons are made with the Marcus-Hush electrochemical theories concerning electrode kinetics. A related section explores procedures for the kinetic analysis of steady state voltammetric data obtained at microdisc electrodes. A method is proposed under the name of Normalised Steady State Voltammetry and is tested using data obtained from a Fast Quasi-Explicit Finite Difference simulation of diffusion to a microdisc electrode. In a second area of work using microelectrodes, the electrochemical behaviour of compounds of the general formula M(CO)3(η3 - P2P1) where M is either Cr, Mo or W and P2P' is bis(2-diphenylphosphinoethyl)phenylphosphine) is elucidated. The development of instrumentation and mathematical procedures relevant to the measurement and quantitation of these systems is also investigated. The tungsten compound represents the first examples where the 17-electronfac+ and mer+ isomers are of comparable stability.

Determination of anabolic steroids by differential pulse polarography

Determination of anabolic steroids often requires the use of elaborate techniques such as gas chromatography - mass spectrometry (GC-MS), gas liquid chromatography (GLC) and more recently high performance liquid chromatography (HPLC). Most of these methods employ derivatisation techniques prior to detection which makes them tedious and relatively time consuming. Other methods demand a great deal of skill. A simple and rapid analytical method, based on differential pulse polarography at a dropping mercury electrode has been developed for the determination of various anabolic steroids in a range of commercially available pharmaceutical preparations. Detailed investigation of the electrochemical behaviour of these steroids was made in order to elucidate the electrode processes involved, in addition to optimising the method. Several other analytical methods such as GC-MS, NMR, ultraviolet (UV), infrared (IR) spectroscopy were also used to confirm the products of the chemical and electrochemical reactions. Possible reactions are suggested. Various extraction procedures were examined for separation of selected steroids from the oil-based or pill matrix and their suitability for polarographic determination is discussed.

A new Lewis-base ionic liquid comprising a mono-charged diamine structure : a highly stable electrolyte for lithium electrochemistry

A new Lewis-base ionic liquid (IL) based on mono-charged 1,4-diazabicyclo[2.2.2]octane (dabco) was synthesized and its thermal and electrochemical behaviour was characterized. The dabco-based IL with bis(trifluoromethanesulfonyl)amide (TFSA) anion melts at 76 °C when the N-substituted alkyl chain length is 2. The dabco-based IL showed a wide electrochemical window of over 4 V ranging from −3.5 to +1.5 V vs. Fc/Fc⁺ and was able to deposit and strip lithium from a nickel substrate at reasonable efficiency.

The electrochemistry of lithium in ionic liquid/organic diluent mixtures

The electrochemistry of lithium is investigated in a number of electrolytes that consist of a lithium salt dissolved in a combined ionic liquid-organic diluent medium. We find that ethylene carbonate and vinylene carbonate improve electrochemical behaviour, while toluene and tetrahydrofuran are less promising.We also present insights into the electrode passivation caused by these diluents in an ionic liquid electrolyte during lithium cycling. We observe that during lithium cycling those electrolytes with carbonate based diluents are the most able to utilise their previously reported improved lithium ion diffusivities. Conversely, tetrahydrofuran, the most promising diluent of those studied in terms of its known ability to increase lithium ion diffusivity is found not to be as advantageous as a diluent. It appears that the poor electrochemical interfacial properties of the tetrahydrofuran electrolyte prevented the realisation of the benefits of the high solution lithium ion diffusivity.

Tin-based composite anodes for potassium-ion batteries

The electrochemical behaviour of a Sn-based anode in a potassium cell is reported for the first time. The material is active at low potentials vs. K/K(+), and encouraging capacities of around 150 mA h g(-1) are recorded. Experimental evidence shows that Sn is capable of alloying/de-alloying with potassium in a reversible manner.

Evaluation of corrosion behaviour of biodegradable base oils using electrochemical techniques

© 2015 Institute of Materials, Minerals and Mining. Published by Maney on behalf of the Institute. This paper describes an interesting attempt to quantitatively evaluate the corrosion behaviour of base oils using a novel approach based on electrochemical techniques. The present study evaluates the corrosion behaviour of biodegradable base oils with and without additives in an aqueous chloride solution using electrochemical measurements. Potentiodynamic polarisation and electrochemical impedance spectroscopy techniques were used to quantitatively determine the corrosion behaviour of these oils, and the results were compared to the conventional immersion tests. Both these electrochemical measurements were carried out in a three-electrode system where AS1020 mild steel alloy was used as a working electrode in a purpose made pipette cell. The results obtained from the electrochemical measurements help to evaluate the best biodegradable base oil for formulating eco-friendly industrial lubricants.

The influence of heat treatment on the corrosion behaviour of as-spun amorphous Al88Ni6La6 alloy in 0.01 M NaCl solution

The effect of the heat treatment on the corrosion behaviour of amorphous Al₈₈Ni₆La₆ made by melt-spun has been investigated by electrochemical measurements. Heat treatment was carried out at 523 K and 673 K for 4 min and 15 min respectively. The evolution of the crystallization process after annealing was identified by differential scanning calorimeter (DSC) as well as X-ray diffraction. The XRD patterns show that the structure of samples heat-treated at higher temperature changes towards a crystal state. The results obtained from the polarization curves reveal that all Al₈₈Ni₆La₆ alloys exhibit spontaneously passivated behaviour. Furthermore, it is noted that the partially crystallized alloy has the best corrosion resistance in comparison with as-spun amorphous and fully crystallized alloys, while the fully crystallized sample shows deterioration in the corrosion resistance.

On the electrochemical response and interfacial properties of steel–Ca(OH)2 and the steel–concrete system measured using galvanostatic pulses

The interfacial properties of the steel–concrete system are examined via a new approach for evaluation of galvanostatic pulse data. This methodology allows for rapid determination of the corrosion activity of steel, and readily yields values for parameters related to corrosion such as the polarisation resistance and interfacial capacitance. The method of analysis is based on the iterative fitting of a non-exponential model based on a modified Kohlrausch–Williams–Watt (KWW) formalism. The transient behaviour of steel in concrete is non-exponential in its form and, when analysed this way, an exponent β can be determined characterising the exponential non-ideality of the transient. This non-ideality parameter is found to differ significantly for actively corroding and passive specimens, thereby serving as a useful index to the level of corrosion being experienced. Furthermore, the investigation of the interfacial characteristics of the system, previously unobtainable in a reproducible manner via other electrochemical methods, reveal information regarding the kinetic factors governing corrosion of steel in concrete.